Inorganic brush and slip-ring assembly



8 0, 1968 G. E. WENDELL 3,398,387

INORGANIC BRUSH AND SLIP-RING ASSEMBLY Filed March 16, 1966 3Sheets-Sheet 1 lA/V'A/TOL g- 20, 1968 G. E. WENDELL 3,398,387

INORGANIC BRUSH AND SLIP-RING ASSEMBLY Filed March 16, 1966 I:Sheets-Sheet 2 jjg 45 5 Aug. 20, 1968 5. E. WENDELL INORGANIC BRUSH ANDSLIP-RING ASSEMBLY 3 Sheets-Sheet 3 Filed March 16, 1966 United StatesPatent O 3,398,387 INORGANIC BRUSH AND SLIP-RING ASSEMBLY George E.Wendell, Blacksburg, Va., assignor to Litton Precision Products, Inc.,Beverly Hills, Califl, a corporation of Delaware Filed Mar. 16, 1966,Ser. No. 534,912 7 Claims. (Cl. 339) ABSTRACT OF THE DISCLOSURE A brushand slip-ring assembly of inorganic composition, the slip-ring assemblyincluding a plurality of identical disclike elements stacked adjoiningone another, each element being provided with a plurality of aperturesand a preformed radial channel in the outer surface, the channelcommunicating with one of the apertures and the outer periphery of theelement, the apertures of adjacent elements being in registration, aplurality of conductors free of organic insulation extending through thealigned apertures with one conductor extending through each radialchannel, circumferential grooves at the junction of adjacent elementsare provided with conductive contacting surfaces in electrical contactwith the corresponding conductor, the brush assembly having one brush incontact with each conductive surface.

The present invention relates to rotating contact assemblies and, moreparticularly, to brush and slip-ring assemblies suitable fortransferring electrical signals or electrical power between relativelyrotating components such as are employed in precision instruments, forexample, in gyroscopic guidance systems.

Of major importance in precision instruments, such as the gyroscopicsystems used to perform indicating or control functions on modern, highspeed aircraft or ships, is the low-noise transmission of low-levelelectrical signals to and from moving and rotating structures. Asignificant source of unwanted electrical fluctuations or noise in suchapparatus is the variation in the resistance between the contacts in thebrush and slip-ring assemblies. It has been determined that, when suchbrush and slip-ring assemblies employ base metal contacts, one cause ofthe variation in the resistance is due to an insulating oxide of thecontact materials which forms on the contacts. Changes in the design ofthe brush and slip-ring assemblies to replace the base metal withprecious metal contacts effectively eliminated the oxides, but failed toprevent the occurrence of the residual variations. Despite continuingefforts of the industry toward the improvement of the materials,processes and designs, the problem continues with only reductions in themagnitude of such resistance variations.

It has been determined that the high fluctuating resistance between thecontacts in the brush and slip-ring assemblies is caused by collectionsof high resistance material in the contact area. The consensus is thatthe film forms from organic materials in the vicinity of the wipedprecious metal contact. The contact material apparently reacts with, orcatalyzes the polymerization of organic materials which reach the noblemetal of the contact. The organic material can travel to the contacteither as a liquid (from plastic wire insulation or from processingresidues) or it can deposit on the contact by vaporized organics fromthe slip-ring insulating material. Once deposited on the metal contact,a reaction occurs and the organic begins to harden into a material ofhigh electrical and chemical resistance. Such related problems causeinadequate contact life which necessitates frequent and expensiveoverhaul and repairs to maintain critical operational tolerances.

It is, therefore, an object of the present invention to provide slidingelectrical contact assemblies capable of reliable, low-noise performancefor relatively extended periods of time.

It is another object of the present invention to improve the operationof sliding contact assemblies by eliminating all organic materialtherefrom.

Experiments heretofore conducted have pointed up certain difiicultiesthat make brush and slip-ring assemblies fabricated of inorganicmaterials seem impractical. First, it has been thought that most glassesand ceramics cannot be formed around components since the workingtemperatures of glass and ceramic materials exceed working temperaturesof the components. This is particularly true with the nonferrouscomponents, such as those made of copper alloys (for example, thelead-in wire) and the gold alloy slip-rings. In the case of componentsmanufactured of fired ceramic materials, the firing temperatures of theceramics are not stable. Second, the ceramic industry has not been ableto produce materials which can be cast, molded or fired to formcomponents having precise dimensions. Most ceramic materials, due toshrink age, change dimensions by a factor of several percent as theformed components cool. Third, because of the hard, abrasive nature ofinorganic materials, heretofore it has been found difiicult to cutgrooves into such material to enable electrodeposition of theslip-rings.

Thus, another object of the present invention is to facilitate thefabrication of inorganic sliding contact assemblies having a longeruseful life and no resistance variations between contact memberstherein.

These and other objects are accomplished in one embodiment of theinvention by a sliding contact assembly wherein the slip-ring assemblyconsists of a supporting shaft on which preformed, high strength, glasswafers or discs are stacked. Each wafer is constructed of an inorganicmaterial which has no out-gasing characteristics at elevatedtemperatures. Each of the preformed wafers has a plurality of holes cuttherethrough parallel to the axis of rotation of the supporting shaftand which are oriented to be in register with corresponding holes inadjacent wafers. When the total number of wafers is stacked on thesupporting shaft, a plurality of channels is formed. Through each ofthese channels an uninsulated lead wire is threaded from one end of theassembly to a respective outlet on a different one of the wafers. Whenthe wafers have been properly oriented on the supporting shaft and thelead wires threaded therethrough, the assembly is heated to atemperature sufiiciently high to cause the wafers to fuse to oneanother. A conductive slip-ring is formed on each wafer so as to be inconductive engagement with its respective lead wire.

Each brush assembly in the embodiment of the invention described hereinis also fabricated of similar inorganic material having channels thereinthrough which uninsulated lead wires are threaded to the points ofconnection to the brushes. The slip-ring assembly and the brushassemblies are enclosed within a housing which substantially preventsexposure of the brush and slip-ring contacts to contaminants of theexternal environment.

These and other advantages and features which are believed to becharacteristic of the present invention, both as to its organization andmethod of operation, will be better understood from the followingdescription con sidered in connection with the accompanying drawings inwhich one embodiment of the present invention is ill-ustrated by way ofexample. It is to be expressly understood, however, that the drawingsare for the purpose of illustration and description only and are notintended as a definition of the limits of the invention.

In the drawings:

FIGURE 1 is a cross-sectional view of a slip-ring capsule constructed inaccordance with the teachings of the present invention;

FIGURE 2 is a partially sectional side view of a slipring and brushassembly which schematically illustrates the engagement of one with theother in a capsule of the type shown in FIGURE 1;

FIGURE 3 is a side view of a partially assembled slipring assemblyshowing slip-ring wafers in stacked relationship to one another having alead wire protruding from each wafer;

FIGURE 4 is a first cross-sectional view of the slipring assembly shownin FIGURE 3 taken at the line 44;

FIGURE 5 is a second cross-sectional view of the slipring assembly shownin FIGURE 3 taken at the line 55;

FIGURE 6 is a vertical cross section of one typical slip-ring wafershowing longitudinal holes and a radial groove cut in the wafer;

FIGURE 7 is a sectional view of one slip-ring showing the formationthereof on a corresponding slip-ring wafer;

FIGURE 8 is a bottom view of one brush assembly shown in FIGURE 2; and

FIGURE 9 is an end View of the slip-ring and brush assembly shown inFIGURE 2.

Reference is now made to the drawings, wherein like or correspondingparts are designated by the same or similar reference charactersthroughout the several views. There is shown in FIGURE 1 a slip-ringcapsule 10 having a housing 11 which surrounds an inorganic slip-ringassembly 12 and a pair of inorganic brush assemblies 30 and 33. Theslip-ring assembly 12 consists of a supporting shaft 15 which carries aplurality of conductive slip-rings 16. The shaft 15 may be fabricated,for example, from stainless steel. Each conductive slip-ring 16 isconnected respective'ly to a wire 40 which is un-insulated and threadedthrough a hole in the slip-ring assembly running from its point ofconnection to slip-ring 16 to a slip-ring reinforcing member 13. Withinthe slip-ring reinforcing member 13 the wires 40 are connectedrespectively to insulated slip-ring lead wires 44 for attachment tosources of electrical signals or power. A detailed description of theconstruction of the slip-rings 16 will be undertaken hereinafter inconnection with FIGURES 2 and 3.

As shown in FIGURE 1, the slip-ring assembly 12 is rotatably supportedwithin the housing 11 by a pair of bearings 20 and 21. A frame member 28holds the bearings 20 and 21 in their proper position within the housing11, such that the bearings engage with a pair of bearing seats 14 and17, respectively, which are mounted on the supporting shaft 15. One endof this supporting shaft 15 has been reduced in diameter and threads 27placed thereon. A nut 23 is threaded on to the threads 27 for urgingagainst a bearing retaining ring 24 which, as the nut 23 is tightened,properly seats the bearing 21 on the bearing seat 17. It will be noticedthat the shaft 15 has been reduced in size at location 25 to allowproper clearance for the bearing retaining ring to mate with bearing 21.The bearing seat 14, located at the opposite end of the slip-ringassembly 12 from the bearing seat 17, is simultaneously positioned withrespect to its corresponding bearing 20 as the nut 23 is tightened onthe threads 27.

The supporting shaft 15 which passes through the bearing seat 14terminates in the slip-ring reinforcing member 13. To secure the shaftwithin the reinforcing member and to provide insulation between theuninsulated lead wires 40, at their point of connection 42 to theslip-ring lead wires 4 the void within the slip-ring reinforcing member13 is filled with a solder glass 18 or Pyroceram Cement No. 95manufactured by the Corning Glassworks of Corning, NY.

The brush block assemblies and 33 are secured in posiiton by theretaining screws 31 and 34, respectively. As may be understood from thedescription which hereinafter follows, a plurality of brushes 60 of thebrush assembly 30 and a plurality of brushes 61 of the brush assembly 33slideably engage with, and receive signals from, the conductiveslip-rings 16. These signals are transmitted 4 from the brushes 60 and61 through lead wires 62 and 63, respectively, to utilization devicestherefor.

Attention is now directed to FIGURE 2 wherein there is shown a partiallysectional side view of the slip-ring assembly 12 and the pair of brushassemblies 30 and 33 forming a part of the slip-ring capsule 10, shownin FIG- URE 1. In accordance with one aspect of the invention, the brushassembly 33 is shown in FIGURES 2, 8 and 9 to include an insulatingmember 37, having a support member 38 attached to one end thereof. Thelead wires 63 terminate within the support member 38 and are connectedto a plurality of conductors 65. Channels cut in the top of theinsulating member 37 are filled with copper, or silver, or gold alloywith a copper coating to form junction bars 59, and one of theconductors 65 is attached to each of the filled junction bars 59. Thebrushes 61 are then soldered to the junction bars 59 such that eachbrush 61 wraps around the insulating member 37 (as shown in FIGURE 8)and slideably engages with one of the sliprings 16 (as shown in FIGURES2 and 9).

The brush assembly 30, which is shown in FIGURES 2 and 9, is constructedsimilar to the brush assembly 33 to include an insulating member 35having a support member 36 attached to one end thereof. The insulatingmembers 35 and 37 together with their respective support members 36 and38 may be constructed of a number of inorganic materials, such asFotoceram, a trademark for a high strength glass of the CorningGlassworks of Corning, NY. The brush assembly 30 is shown in FIGURE 2 tohave a plurality of junction bars 58 to which the brushes 60 aresoldered. A corresponding plurality of conductors 64 couple the junctionbars 58 to the brush block leads 62, the insulation of the brush blockleads 62 terminating within the support member 37 of the brush assembly30. Alternatively, the brushes 60 and 61 may be cast into the brushblocks at the time the brush blocks are formed. Thus, no organicmaterials, such as those used for wire insulation and heretofore forbrush blocks, are used in the area of contact between the brushes andsliprings.

Attempts to manufacture slip-ring and brush assemblies using glass orceramic materials heretofore have been unsuccessful because of the acuteproblems associated with machining and handling the glass or ceramicmaterials, holding the required dimensions of components manufacturedfrom such materials, and with the high temperatures at which glass orceramic materials are fired or worked. These problems have restricted,and in most cases precluded, the use of glass or ceramic in brush andslip-ring assemblies.

However, in recent years, form-grinding techniques have been perfectedto the point where they may be applied to solve the problem of machiningglass and ceramic materials for use in slip-ring assemblies. Thus,directing attention to FIGURES 2 through 6, and in accordance withanother aspect of the present invention, the slip ring assembly 12comprises a number of discs, or wafers, 50 fabricated of inorganicmaterial, such as Fotoceram glass, and stacked on and attached to thesupporting shaft 15. A typical wafer, as shown in FIGURES 5 and 6, isfabricated to have a number of longitudinal holes 46 formed orchemically machined through the glass wafer 50 parallel to the axis ofrotation of the supporting shaft 15. A number of wafers 50 are stackedon the supporting shaft 15 and oriented so that the holes 46 of eachwafer are in register to form longitudinal channels through which leadwires 42 may be threaded. The number of longitudinal holes 46 which arecut through each wafer 50 corresponds to the number of slip-rings 16 tobe included in the slipring assembly 12. Moreover, as shown in FIGURES 5and 6, a radial groove 51 is cut or formed from one of the longitudinalholes 46 (such as the radial groove 51 connected to a longitudinal hole48) to the outer circumference of the wafer. One lead wire of theplurality of lead wires 42 (such as a lead wire 45 passing through thehole 48) is threaded through corresponding ones of the longitudinalholes and then bent so as to exit the stack of Wafers 50 through one ofthe radial grooves 51.

Glass spacing wafers 54 are positioned on one side of the stack ofslip-ring wafers 60; and, on the other side of the stack of slip-ringwafers 50, an insulating wafer 52 (having a corresponding number oflongitudinal holes 46 cut therein) is positioned on the shaft such thatthe longitudinal holes 46 therein will be in register with thelongitudinal channels formed by the stack of wafers 50. Once the wafers50, 52, and 54 are stacked on the supporting shaft 15 and oriented tohave the lead wires 42 (including the lead wire 45, for example) passingthrough the longitudinal channels, the assembly is heated to atemperature of approximately 800 centigrade in order to fuse the waferstogether. Alternatively, the assembly could be sealed with solder glassof Pyroceram Cement No. 95 manufactured by the Corning Glassworks ofCorning, N.Y. Pyroceram Cement may also be used, for example, to attachthe glass wafers to the shaft 15.

Thus, by either heating or coating the stacked slip-ring wafers withsolder glass or Pyroceram Cement, the wafers 50, 52 and 54 are joined toform essentially one homogeneous mass through which each of the leadwires 42 extend from one end of the stack to its respective radialgroove 51. For example, FIGURE 5 illustrates a crosssection of thepartially-assembled slip-ring assembly 12 taken at the line 55 of FIGURE3. It may be seen that the lead wire 45 has been threaded through thebearing seat 14, the wafer 52, and through each of the wafers 50 to thelocation of the last wafer 50 in the stack. The lead wire 45 is threadedup through the radial slot 51 in the last wafer 50.

To form the actual slip-rings 16, then, circumferential grooves areground into the outer surface of the fused glass wafers with a spacingbetween grooves such that an end of one lead wire 42 is exposed in thebottom of each groove. With reference to FIGURE 7, for example, in orderto form one of the slip-rings 16, the end of the lead wire 45 has asmall amount of copper electro-formed thereon. Next, a thin layer ofelectroless copper is reduced into the groove. More copper is :plated ontop of the electroless copper. A layer of metal, such as nickel, iselectroformed or deposited on the surface of the assembly and into thecircumferential groove to a depth of less than ten millionths of aninch. The thin layer of nickel is then removed everywhere except in thebottom of the groove by any one of a number of well known methods, suchas grinding. Gold is then electrodeposited on the thin nickel layer inthe bottom of the groove until the groove is filled with gold. Thesurface of the slip-ring assembly is ground to remove the excess goldand a thin layer of glass, thereby making the slip-rings flush with theadjoining glass surfaces. A V-groove 56 is cut into the deposited goldto form a slip-ring of the type described and claimed in the copendingapplication of James Carl Davis for Multitrack Slip-Rings, Ser. No.434,976.

Although the invention is illustrated in the embodiment of FIGURES 2 and7 having a particular electrodeposited construction with a V-shapedgroove or channel therein, it will be appreciated that other metals andchannels having other cross-sections which are wider at the top andnarrower at the bottom may also be used. Yet other types of channelsadapted to receive a brush in sliding conductive contact with thechannel walls may also be employed, such as channels which varyarbitrarily over their depth from a maximum to a minimum width.

Miniature brushes of the type employed in the present invention, such asthe brushes 60 and 61 shown in FIG- URE 2, may be fabricated from a goldalloy material sold under the trade name of Meyoro 28A, produced by theJ. M. Mey Company of Broomfield, Conn. It has been found that byemploying both a precious metal (gold) slip-ring 16 and a set ofprecious metal brushes 60 and 61, the most frequently noted failures inslip-ring assemblies, due to the formation of insulating oxides, can beeliminated. Moreover, by employing the totally inorganic constructiontechnique of the present invention, which eliminates the use of allorganic materials from the inside of the slip-ring capsule 10,additional improvements in the operation of the brush and slip-ringassembly are obtained.

To obtain even greater reliability in the operation of the precisionslip-ring capsule 10, each of the brushes 69 and 61 (which may also takethe form of a formed brush 57, shown in FIGURE 7) makes contact with itsrespective slip-ring 16 at two locations spaced approximately apart.Such an arrangement (shown in FIGURES 2 and 9) provides four contactareas, two for each brush, with the Vgroove of the slip-ring 16; and,because inorganic materials have been effectively eliminated from theinside of the slip-ring capsule 10, the assembly operates withsignificantly less electrical noise caused by fluctuations in thecontact resistance. Moreover, by minimizing the exposure of the contactsto contaminating organics from the capsule assembly itself, and byminimizing the exposure of the contacts to environments external to thecapsule so that no gas How can occur through the assembly, the onlycontaminants which reach the contact surfaces are those attributable toair flow into the capsule as -a result of a breathing action, which isless likely to represent a serious source of contaminants.

It is to be understood that the above-described arrangements areillustrative of the application of the principles of the invention.Numerous other arrangements may be devised by those skilled in the artwithout departing from the spirit and scope of the invention. Thus, byway of example and not of limitation, brushes and grooves of varioussizes and cross-sectional configuration may be employed to achievemulti-track contact :as taught herein by example. Additionally, otherinorganic materials having characteristics comparable to those ofFotoceram glass may be used to fabricate the insulating base for theelectroformed slip-rings. Accordingly, from the foregoing, it

is evident that various changes may be made without deh parting from thespirit of the invention as defined in the appended claims.

What is claimed as new is:

1. A sliding contact assembly comprising:

a plurality of inorganic disc-like elements, each of said elements beingidentical in size and configuration and being provided with a pluralityof apertures extending therethrough and a radial channel in the outersurface thereof, said channel communicating with one of said aperturesand the outer periphery of said element, said elements being stackedadjoining one another with the apertures thereof in registration withapertures in the adjoining element;

a plurality of conductors free of organic insulation extending throughthe registered apertures with one of said conductors extending througheach said radial channel to the outer periphery of the correspondingelement;

circumferential grooves on the periphery of said elements adjacent thejunction of adjoining elements, each of said grooves having at least oneof said conductors communicating therewith; and

conductive contacting surfaces within said grooves in electrical contactwith the corresponding conductor.

2. The sliding contact assembly as defined in claim 1, wherein saidplurality of disc-like elements are ceramic and are inorganically bondedtogether to form essentially a homogeneous cylinder.

3. The sliding contact assembly as defined in claim 1, wherein saidplurality of disc-like elements are ceramic and are fused together toform essentially a homogeneous cylinder.

4. The sliding contact assembly as defined in claim 1, which furtherincludes:

an inorganic brush block positioned adjacent said stacked elements andhaving a plurality of brush block conductors free of organic insulationthreaded therethrough; and

a plurality of noble metal brushes supported by said brush block andrespectively connected to said brush block conductors, each of saidbrushes being in sliding conductive contact with a separate one of saidcontacting surfaces.

5. The sliding contact assembly as defined in claim 1,

which further includes:

a rotatable support member, said plurality of disc-like elements beingaffixed to said support member.

6. A method of making a sliding contact assembly, in-

cluding the steps of:

preforming a plurality of disc-like elements from inorganic material tohave a radially extending channel in the outer surface thereof;

stacking said elements on a supporting member so that they arecontiguous with one another with each of said channels engaging thesurface of an adjoining element to form a radial aperture;

threading conductors free from organic insulation through respectiveapertures with the ends of said conductors terminating at least adjacentto the periphery of the corresponding element;

inorganically bonding the stack of disc-like elements to form a rigidcylinder;

grinding circumferential grooves in the periphery of said elements toremove a portion of the ends of said conductors; and

forming conductive contacting surfaces within said grooves in electricalcontact with respective conductors.

8 7. A method of making a sliding contact assemblyas set forth in claim6 which further includes the steps of:

forming said disc-like elements to be identical and to have a pluralityof holes through each element, each of said channels communicating withone of said holes and the periphery of its corresponding element;

orienting said elements so that said plurality of holes are in registerto form a corresponding plurality of longitudinal apertures through thestack of elements with a different one of said channels extending froeach longitudinal aperture;

threading said conductors through respective longitudinal apertures, oneend of each conductor being threaded out through a corresponding radialchannel; and

fusing the stack of disc-like elements to form a rigid cylinder.

References Cited UNITED STATES PATENTS 2,458,552 1/1949 Blattner 339-2782,494,244 1/1950 JOnard et al 3395 2,874,362 2/1959 Blanding 33953,095,252 6/ 1963' Adkins 339- 3,219,557 11/1965 Quintana 3 39'-53,297,973 1/1967 Wendell 3395 30 MARVIN A. CHAMPION, Primary Examiner.

R. S. STROBEL, Assistant Examiner.

